A presettable counter with indicating rollers generally serves to issue once or as many times as desired via suitable presetting means a preset quantity for instance at a liquid dispensing station. Such presettable counters are mostly used in combination with a quantity counter in such manner that the quantity counter counts the quantity delivered starting at zero counting position while the presettable counter is driven in the reverse direction in synchronism with the quantity counter from the preset position to zero position U.S. Pat. No. 3,031,103). Most devices of this kind are of such design that whenever the desired quantity is preset right from the beginning of the delivery, the presetting means can no longer be operated due to a locking device. When the quantity to be delivered gradually assumes the preset value a valve, by being gradually operated, reduces the quantity flow and is completely closed as soon as the preset volume has been reached. The locking device which was effective during the delivery then releases the presetting device so that selectively the delivery process can be repeated with the same preset quantity or a new quantity to be delivered can be preset. This device is disadvantageous in that for moving the presettable indicating roller to its preset position the switching lever is manually actuated to produce the kinetic energy and directly and positively engages the setting wheel which is in the shape of a ratchet wheel. This means that the presettable counter in order to be preset must be designed to be resistant to all sorts of mechanical action, while also being resistant to heavy blows in order to be able to function under all circumstances. When considerable force is exerted on the indicating rollers in being switched in a step by step manner, they tend to overthrow. In that case damages to the switching pawl and the ratchet wheel are practically unavoidable so that the presetting device may become inoperative.
In another known presettable counter, as disclosed in DAS No. 1,207,119 the setting means for the presettable counters are in the form of slides or key shafts to be moved backwards and forwards and they are provided with pivoting pawls in direct engagement with the toothing of the ratchet wheel. When the key returns to its initial position the switching pawl, which is drawn by a spring to a stop bolt, can evade by overcoming the spring action. In order to make sure that during the delivery process the mechanical operation within the counter is neither disturbed nor blocked by the operation of the keys in the known device the shafts of the presetting keys cooperate with locking means which are out of engagement only when the resetting means of the counter mechanism is operated.
It is obviously disadvantageous to apply the setting energy directly to the presettable indicating rollers. But the arrangement of a locking device in connection with the key shafts which at least avoids an erroneous actuation of the keys and thereby damage to the counter brings about an additional risk. For instance, by a wrong operation of the setting device of the counter by violently actuating the keys in their locked condition under the impression that the keys can only be operated by applying heavy force, considerable damage can be applied to the mechanical parts of the presettable counter.
In DAS No. 1,524,582 a setting device for a presettable counter has been described in which the switching pawl is arranged to be tilted in order to avoid detrimental effects to the counter at least as long as the setting device is in its locked state. To this end the switching pawl is mounted on a pivotal bracket which temporarily moves the switching pawl out of engagement with the ratchet wheel by means of a sliding lever connection. Apart from the fact that the switching pawl is ineffective in its locked state the full setting energy will be applied undamped to the presetting roller due to a direct engagement between the key and the toothing of the setting wheel. When the presetting energy is applied to the switching pawl and the ratchet wheel by a heavy blow, for instance by a violent actuation of the key, the indicating roller tends to overthrow or there is a risk that the mechanical connections are destroyed. Therefore, also with this known presetting device it is not made sure that for each operation of the key the corresponding indicating roller of the presettable counter is moved by one step and thereby one indicating position only.